Droplet microfluidics for chip-based diagnostics.

Droplet microfluidics (DMF) is a fluidic handling technology that enables precision control over dispensing and subsequent manipulation of droplets in the volume range of microliters to picoliters, on a micro-fabricated device. There are several different droplet actuation methods, all of which can generate external stimuli, to either actively or passively control the shape and positioning of fluidic droplets over patterned substrates. In this review article, we focus on the operation and utility of electro-actuation-based DMF devices, which utilize one or more micro-/nano-patterned substrates to facilitate electric field-based handling of chemical and/or biological samples.

Liquid DEP actuation and precision dispensing of variable volume droplets.

Droplet based microfluidic systems, in recent years, have demonstrated numerous advantages and exciting potential for Lab-On-a Chip applications. In order to fully realize the potential benefits of this technology, one requires precision dispensing and manipulation of droplets of known volume and sample concentration, in a rapid and controlled manner. In this article, we demonstrate the rapid and controlled microactuation of aqueous samples and subsequent dispensing of variable volume droplets in nanolitre to picolitre regime by using a coplanar tapered electrode structure that leverages the phenomena of liquid dielectrophoresis (L-DEP).

Liquid dielectrophoresis and surface microfluidics.

Liquid dielectrophoresis (L-DEP), when deployed at microscopic scales on top of hydrophobic surfaces, offers novel ways of rapid and automated manipulation of very small amounts of polar aqueous samples for microfluidic applications and development of laboratory-on-a-chip devices. In this article we highlight some of the more recent developments and applications of L-DEP in handling and processing of various types of aqueous samples and reagents of biological relevance including emulsions using such microchip based surface microfluidic (SMF) devices. We highlighted the utility of these devices for on-chip bioassays including nucleic acid analysis.

Polarizability of red blood cells with an anisotropic membrane.

We predict the complex polarizability of a realistic model of a red blood cell (RBC), with an inhomogeneous dispersive and anisotropic membrane. In this model, the frequency-dependent complex electrical parameters of the individual cell layers are described by the Debye equation while the dielectric anisotropy of the cell membrane is taken into account by the different permittivities along directions normal and tangential to the membrane surface. The realistic shape of the RBC is described in terms of the Jacobi elliptic functions.

DEP actuation of emulsion jets and dispensing of sub-nanoliter emulsion droplets.

Liquid Dielectrophoresis (L-DEP) has been successfully leveraged at microscopic scales and shown to provide a controllable means of on-chip precision dispensing and manipulation of sub-nanoliter single emulsion droplets. In this paper, we report on the dynamics of a DEP actuated emulsion jet prior to break-up and compare its characteristic behavior based on the lumped parameter model of Jones et al. (R.

Microfluidic device for dielectrophoresis manipulation and electrodisruption of respiratory pathogen Bordetella pertussis.

A miniaturized microfluidic device was developed to facilitate electromanipulation of bacterial respiratory pathogens. The device comprises a microchip with circular aluminum electrodes patterned on glass, which is housed in a microfluidic system fabricated utilizing polydimethylsiloxane. The device provides sample preparation capability by exploiting positive dielectrophoresis (DEP) in conjunction with pulsed voltage for manipulation and disruption of Bordetella pertussis bacterial cells.

Leveraging liquid dielectrophoresis for microfluidic applications.

Miniaturized fluidic systems have been developed in recent years and offer new and novel means of leveraging the domain of microfluidics for the development of micro-total analysis systems (microTAS). Initially, such systems employed closed microchannels in order to facilitate chip-based biochemical assays, requiring very small quantities of sample and/or reagents and furthermore providing rapid and low-cost analysis on a compact footprint. More recently, advancements in the domain of surface microfluidics have suggested that similar low volume sample handling and manipulation capabilities for bioassays can be attained by leveraging the phenomena of liquid dielectrophoresis and droplet dielectrophoresis (DEP), without the need for separate pumps or valves.

Ingestible capsule for impedance and pH monitoring in the esophagus.

Twenty-four-hour ambulatory pH monitoring is an essential tool for diagnosing gastroesophageal reflux disease (GERD). Simultaneous impedance and pH monitoring of the esophagus improves the detection and characterization of GERD. Conventional catheter-based monitoring systems are uncomfortable and interfere with the normal activity of the patient.

Integrated microfluidic systems for sample preparation and detection of respiratory pathogen Bordetella pertussis.

An integrated microfluidic system for combined manipulation, pre-concentration, and lysis of samples containing Bordetella pertussis by dielectrophoresis and electroporation has been developed and implemented. The microfluidic device was able to pre-concentrate the amount of B. pertussis cells present in 200 microl of a B.

Electro-disruption of Escherichia coli bacterial cells on a microfabricated chip.

A miniaturized system for sample preparation of relevant bacterial pathogens has been developed using a variety of microfabrication techniques. The system manipulates and disrupts Eschericha coli bacterial cells using dielectrophoresis, electroporation and enzymes. The microchip consisted of circular gold electrodes patterned on glass using standard photolithography housed in a PDMS chamber.

Continuous dielectrophoretic cell separation microfluidic device.

We present a prototype microfluidic device developed for the continuous dielectrophoretic (DEP) fractionation and purification of sample suspensions of biological cells. The device integrates three fully functional and distinct units consisting of an injector, a fractionation region, and two outlets. In the sheath and sample injection ports, the cell sample are hydrodynamically focused into a stream of controlled width; in the DEP fractionation region, a specially shaped nonuniform (isomotive) electric field is synthesized and employed to facilitate the separation, and the sorted cells are then delivered to two sample collection ports.

A combined dielectrophoresis, traveling wave dielectrophoresis and electrorotation microchip for the manipulation and characterization of human malignant cells.

The study of the dielectric properties of micrometer- or nanometer-scale particles is of particular interest in present-day applications of biomedical engineering. Electrokinetics utilises electrically energised microelectrode structures within microfluidic chambers to noninvasively probe the physiological structure of live cancer cells. A system is described that combines the three complementary techniques of dielectrophoresis (DEP), travelling wave dielectrophoresis (TWD) and electrorotation (ROT) for the first time on a single, integrated chip (3 x 6 mm).

Electrorotation of axolotl embryos.

The frequency dependent dielectric properties of individual axolotl embryos (Ambystoma mexicanum) were investigated experimentally utilizing the technique of electrorotation. Individual axolotl embryos, immersed in low conductivity media, were subjected to a known frequency and fixed amplitude rotating AC electric field and the ensuing rotational motion of the embryo was monitored using a conventional optical microscope. None of the embryos in the pregastrulation or neurulation stages of development exhibited any rotational motion over the field frequency range (10 Hz-5 MHz).

Theoretical Model of Electrode Polarization and AC Electroosmotic Fluid Flow in Planar Electrode Arrays.

Strong frequency-dependent fluid flow has been observed near the surface of microelectrode arrays. Modeling this phenomenon has proven to be difficult, with existing theories unable to account for the qualitative trend observed in the frequency spectra of this flow. Using recent electrode polarization results, a more comprehensive model of the double layer on the electrode surface is used to obtain good theoretical agreement with experimental data.